Could You Be Allergic to a Joint Implant?

Here's what you need to know before joint replacement surgery.

| By Stephanie Watson

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More than a million hip and knee joints are replaced each year, most of them due to osteoarthritis (OA). These procedures are generally safe and effective for the right candidates. Yet, there have been media reports of people having allergic reactions to the metals used in joint implants. But metal implant allergies are uncommon, says Joshua J. Jacobs, MD, chair of the department of orthopaedics at Rush University. Dr. Jacobs discussed the issues related to metal sensitivity to joint implants at the 2012 annual meeting of the Association of Bone & Joint Surgeons. “I think metal implant allergy is a real entity, but it happens very rarely,” he says.

Metal Joints and Allergies

Prosthetic parts used to replace a damaged knee, hip, or shoulder joint in the U.S. are made from —o r contain metal, because of its durability and the fact that it can stay intact inside the body without corroding. Chromium, nickel, cobalt, titanium and molybdenum are among the most common metals found in implants. Often, a prosthetic joint will contain more than one of these metal types. A very small number of Americans are allergic to one or more metals, with nickel allergy as the most common metal sensitivity.

What’s less clear is how often allergic reactions cause problems for people with metal joint implants. Studies have shown that in some people with a metal allergy, the metal in the implant triggers an immune reaction when it comes into contact with body fluids. When the circulating blood containing traces of the metal reaches the skin, it causes an irritation centered around the implant site, possibly swelling, a rash or blister.

The reaction can be systemic, a delayed response to the metal caused by specialized immune cells called T cells. The evidence about body-wide symptoms has been mainly anecdotal. There have been reports of a Georgia woman who had systemic symptoms due to a metal contact allergy after knee replacement surgery, as well as of an artist who developed body-wide symptoms after a double knee replacement and a Denver woman who reacted to a metal hip implant.

Symptoms of a body-wide (systemic) reaction that have been reported in these types of cases include pain or loss of function in the implant area, weakness or fatigue, diarrhea and headaches.

Doctors say the body-wide type of reaction is rare.

Should You Be Tested Before Implant Surgery? If you are going to have joint replacement surgery, ask your doctor if you should have an allergy test. Because metal allergies are relatively rare, testing before joint replacement surgery isn’t recommended for everyone, says Dr. Jacobs. However, if you’ve had a skin reaction to metal jewelry in the past, you probably should be tested.

Tests for Metal Allergies

The most commonly used test to diagnose a metal allergy is skin patch testing. Very small amounts of various metals are placed on your skin and then covered with a patch. After a couple of days, your doctor removes the patches. If the area is irritated, you are likely allergic to that metal. Skin patch testing is not 100% accurate, though. It is possible to have a false negative or false positive result. This means the test finds that you don’t have an allergy when you actually do, or vice versa.

Researchers at National Jewish Health in Denver say they've developed a new blood test that can more accurately diagnose nickel allergies before implant surgery. This test has been validated against the skin patch test, and the developer, Karin Pacheco, MD, associate professor in the Division of Environmental and Occupational Health Sciences, says it works equally as well, but there is limited research to confirm its effectiveness.

The blood test can also detect the degree to which the immune system is stimulated. “That can be helpful in terms of trying to grade the response,” Dr. Jacobs says. As of March 2014, the nickel allergy blood test is currently only available at National Jewish Health. However, doctors elsewhere in the country can send a patient’s blood sample to the center to be tested.

Another available metal allergy test is called MELISA (memory lymphocyte immunostimulation assay). Like Dr. Pacheco’s test, it looks for a white blood cell reaction against the possible metal allergens. But the MELISA test has not been validated against patch testing.